High velocity tensile machinery



Feb. 21; 1950 A. NADAI 2,498,291

HIGH-VELOCITY TENSILE MACHINERY Filed June 2, 1947 $1 /6 w Cf, 7 .4.

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ATTORNEY Patented Feb. 21, 1950 UNITED STATES PATENT "()IFFICE 9 Claims.

This invention relates to apparatus for determining the characteristics of metals or other materials under rapidly applied impact forces of ,sufficientstrength to break the material.

More particularly, this invention relates to an improvement in the type of apparatus disclosed in United States Patent No. 2,323,724, issued ,July 6, 1943, to Arpad Nadai and Michael J.

Manjoine.

In the apparatus disclosed in the patent referred to above, there is shown a support for a specimen to .be "tested together with a rapidly rotating flywheel carrying hammer-like striking devices which are movable to a position in which they are operable to strike the specimen a blow of sufiicient force to break the specimen. The disclosure of this patent also illustrates apparatus by which the force applied'to the specimen and its elongation may-be recorded in the form of a stress-strain graph from which the characteristics under impact of the material being tested maybe determined. It is pointed out in this patent that the support for the specimen being tested must have a high natural frequency of vibration in the nature of 10,000 cycles per second or upwards in order to get a satisfactory stressstrain indication. In the use of such apparatus,

it has been found that the oscillations set up by in undesirable P the acquisition of intelligent data as to the characteristics of the specimen being tested, it is desirable to eliminate or at least reduce the size of such irregularities which are violent oscillations .of an elastic nature superimposed on the desired stress-strain curve. This invention, accordingly, has as its principal object the provision of an improved construction which will materially reduce the irregularities referred to.

In the drawing there is shown a preferred enrbodiment of the invention. In this showing:

Figure l is a perspective view of apparatus for applying an impact forceto a specimen;

Fig. 2 is a stress-strain curve showing the results obtained without the improvement provided by this invention;

Fig. 3 is an enlarged sectional view through the anvil or force receiving element attached to the end of the specimen; and

Fig. 4 is a broken away view, partially in sec tion, of oneof the hammers shown injFig. 1 illustratingthe applicationthereto of the novel subject matter .of this invention.

Referring to Figure 1, there is shown a flywheel 5 which is driven 'by a shaft '2 from a motor 3. A pair of force applying members or hammers 4 are pivotally :mounted on the fiywheel I for movement by a biasing spring 5 to the position illustrated in which the hammers engage with abutments'ii. The hammers 4 are normally, held;in a retracted position against the bias of the springs 5 by trigger mechanism 1. A specimen B-is mounted on'a supporting structure 0 and is provided with a force receiving memher or anvil it at is lower end. .In operation,

the hammers 4 are held in a retracted position and the flywheel l is brought up to the desired speed by the motor 3. The trigger mechanism l is then operated to release the hammers for movement to the position illustrated in which they are operative to engage the anvil l0 and break the specimen '8. The parts thus far described are all shown in Patent No. 2,323,724 referred to above and to which reference is made for a more complete-description thereof, and for a disclosureof the apparatus by which the force applied to and elongation of the specimen is utilized to produce a stress-strain curve such as shown in Fig. 2.

In Fig. 2, there is shown a stress-strain diagram having maximum peaks H and minimum peaks [2 in the initial portion of the curve. The curve is more or less typical of the results obtained by the use of the patented apparatus referred to, although the peaks are somewhat exaggerated for the purposes of this description. These peaks are due to the oscillatory movements of the support 9 for the specimen 8 and the elasticity of the force applying elements t force receiving elements H] including the parts associated With such elements and within the tensile test specimen itself. These vibrations damp themselves out in a comparatively short period of time formost materials tested so that only a few vibrations appear in the initial portion of the stress-strain curve. The peaks are caused .by the fact that the rapidly rotating hammersl apply a sudden finite velocity to the head of the specimen 8 practically instantaneously. Such a sudden application'of a finite velocity must be.

posed elastic oscillations of thesystem.

Referring to Fig. 3, there is shown an im-- proved construction which is operative to eliminate or materially reducethe size ofthepeaks 3 II and I2 in the initial portion of the curve shown in Fig. 2. In this showing, it will be noted that the anvil II] is connected to the specimen 8 by a coupling member l3 having a threaded connection with the specimen 8 and a member 14 projecting upwardly from the anvil II]. The lower end of the member I4 has a threaded connection with a plunger I5 receivable in a cylindrical opening I6 formed in the body of the anvil ID. The space between the upper surface of the plunger I5 and the inner end of the opening I6 as viewed in Fig. 3 is filled by annularshaped layers I'I formed of a resilient material having high internal damping characteristics, such as rubber, leather, lead, etc., separated by thin metal discs IS. The entire assembly is held together by a cap II! at the base of the anvil I0.

With the construction shown in Fig. 3, the hammers 4 upon striking the anvil III will first operate to compress the layers of resilient mate,- rial I'I. This results in a more gradual application of the impact force to the specimen 8 than is had in the case where the anvil II] is rigidly secured to the specimen 8. It is believed that the resilient members IT, in effect, operate to absorb the shock of the initial impact of the hammers I on the anvil II]. Although a hard and not porous rubber may be used in forming the members I! for the purpose of this invention, any similar hard resilient material which offers high resistance to compressive forces and has the quality of high internal damping characteristics may be employed.

Although it is preferred that the shock absorbing members I I be mounted on the force receiving member In as shown in Fig. 3, the shock absorbing devices may be mounted on the force applying member as shown in Fig. 4. In this showing, the striking face of one of the hammers 4 is shown provided with alternate strips of resilient material Il and metal I 8'. This construction will function in like manner to absorb 0r cushion the shock of the initial impact of the hammers 4 on the anvil l0. Both constructions will be found to materially reduce the irregularities in the initial portion of the stress-strain curve.

Since numerous changes may be made in the above-described construction and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all matter contained in the foregoing description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. In apparatus for applying an impact force to a test specimen, a force receiving element connected directly to said specimen, a force applying element movable at a high velocity relative to said force receiving element to subject said specimen to a rapidly applied impact force, and a shock absorbing device comprising a resilient medium, carried by one of said elements, which is compressible by the action of said force applying element to cushion the initial application of force to said specimen.

2. In apparatus for applying an impact force to a test specimen, a force receiving element connected directly to said specimen, a force applying element movable at a high velocity, said elements having surfaces movable relative to each other for applying an impact force to said specimen, and a shock absorbing device comprising a resilient medium on at least one of said surfaces which is compressible by the action of said force applying element to cushion the initial application of force to said specimen.

3. In apparatus for applying an impact force to a test specimen, a support for the specimen having a high natural frequency of vibration, a force receiving element connected directly to said specimen, a force applying element movable at a high velocity relative to said force receiving element to subject said specimen to a rapidly applied impact force, and a shock absorbing device comprising a resilient medium, carried by one of said elements, which is compressible upon operation of said force applying element to apply force to said force receiving element, the compression of said medium being effective to apply the impact force to said specimen in a gradual manner for damping oscillations due to the natural vibrational frequency of said support. I

4. In apparatus for applying an impact force to a test specimen, a support for the specimen having a high natural frequency of vibration, a force receiving element connected directly to said specimen, a force applying element movable at a high velocity, said elements having surfaces movable relative to each other for applying an impact force to said specimen, and a shock absorbing device on at least one of said surfaces for cushioning the initial application of force to said specimen.

5. In apparatus for applying an impact force to a test specimen, a support for the specimen having a high natural frequency of vibration, a force receiving element connected directly to the specimen, a flywheel rotatable at a high velocity, a force applying element mounted on said flywheel, said elements having surfaces movable relative to each other for applying an impact force to said specimen, and a shock absorbing device on at least one of said surfaces for cushioning the initial application of force to said specimen.

6. Apparatus as claimed in claim 5 wherein said shock absorbing device comprises a resilient material having high internal damping characteristics.

7. Apparatus as claimed in claim 5 wherein said shock absorbing device comprises alternate layers of sheet metal and a resilient material having high internal damping characteristics.

8. In apparatus for applying an impact force to a test specimen, a support for the specimen, a force receiving element for applying an impact force to said specimen, a flywheel rotatable at a high velocity, a hammer carried by said flywheel for applying a force of impact proportions to said receiving element for transmission to said specimen, and a shock absorbing device comprising a resilient medium, positioned on said hammer so that in use it is disposed between said hammer and said support, which is compressible by the force transmitted to said specimen, the compression of said medium being effective to cushion the application of force to said specimen.

9. In apparatus for applying an impact force to a test specimen, a rigid support to which the specimen is connected, and means for applying a force of impact proportions to the specimen comprising a rod for connection to the specimen at a point remote from its connection to said support, a collar on said rod, an anvil mounted on said rod for movement relative thereto, a flywheel rotatable at a high velocity, a hammer carried by said flywheel and adapted to strike said anvil an impact blow, and a shock absorbing device comprising a resilient medium, disposed on said anvil to thus in operation be disposed between said anvil and collar which is compressible by relative movement between said anvil and collar, in response to said hammer striking said anvil, the compression of said resilient medium being effective to cushion the application of the 5 impact force to said specimen.

ARPAD NADAI.

REFERENCES CITED The following references are of record in the me of this patent:

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